Easily worth the 40 bucks. Amazing characters, great art and story, perfect sound track, gameplay is fun, and you can do so much with it.
In regards to dlc, money dlc is super nice. If you want to max stats for post-game, you probably want both of the temples (you only need the last one technically but you'd have to level your units enough to where max stats may be harder to get without overclass. If you have both, you can solo the first one with a mercenary that can villager loop). Cipher DLC is 4 characters and it's the cheapest DLC so that's definitely worth it imo. Grinding DLC really isn't necessary since you can just grind in dungeons. Enemies attack you in dungeons (versus them not initiating in grinding DLC) so if you're wanting to solo grind one unit, it's much easier to dungeon grind. If you're grinding your whole team, the dlc map is kinda nice for quick autobattle-esque grinding but that's it.

There are some situations where you want to promote ASAP while other situations where it's kind of... eh?
As an example: Gray is a Villager you get at Lv. 5. He will also be your main (potentially only) Mercenary promotion out of the starting villagers, as it's by far his best class. The base stats for Mercenary are as follows:
24 HP, 8 Str, 8 Skl, 10 Spd, 0 Lck, 4 Def, 1 Res
Gray's base stats are as follows:
24 HP, 9 Str, 4 Skl, 4 Spd, 2 Lck, 4 Def, 2 Res
That means that when you decide to promote him to his inevitable Mercenary, if you do it immediately, he will gain 4 skill and 6 speed. This is a situation where you don't want to waste time trying to get level ups, as instant promotion will help Gray become WAY more useful IMMEDIATELY.
If you don't gain much from promoting, you can probably stay in the class a bit. Example exceptions would be things involving spell lists (ex. If you want Faye's Dancer spell ASAP) or if you want to go into a high movement class (ex. Villager -> Cavalier)

I want to do a run through of all three paths with only Shigure's and Shiro's. As such, I need as many of these guys as possible via Castle Address. Preferably no levels gained and as low of a recruitment level as possible. If you want to give me a Shigure or Shiro, just state which one you're giving and who their parents are, leave your castle address, and make it an easy sieze. If you do all three, I'll definitely leave you an accessory/compliment your castle/what have you. Using a heart seal to put them in their third class (the class they get from the other parent) would be nice, but it's not required at all! Anyone wanna help me out?

The thing with gay fates is that it edits the support table in the hex coding pretty hard, so if you import a save file into the gay fates hack that wasn't originally a gay fates save file, your supports are going to get flopped around. It's highly recommend to start a new save when playing gay fates.